Polycarbonate resins have excellent transparency and heat resistance, and low moisture absorption, and so are good as optical materials. In the manufacture of optical products such as compact disks or laser disks, there is a need for continuous production. The polycarbonate resins used for such products must therefore also have excellent mold release characteristics. And because they are molded at high temperatures, in excess of 300.degree. C., the polycarbonate resins must have high thermal stability.
Polycarbonates are usually manufactured by the phosgene process. However, polycarbonates obtained in this way have the drawback of poor mold release, which complicates the continuous production of molded products from them. Polycarbonate compositions containing various added mold release agents are known, but those compositions have problems when it comes to thermal stability.
In addition, conventional polycarbonate resins tend to become discolored when they are molded. Optical materials should be both transparent and also free of optical distortion. In order to obtain moldings with less optical distortion, the molding temperature can be increased, or resins with lower average molecular weights can be used, to obtain better melt flow and thus minimize formation of optical inhomogeneities. However, increasing the resin temperature during molding tends to cause more discoloration due to polymer degradation. Using polycarbonates with lower average molecular weights can result in pronounced molecular weight lowering and discoloration during molding, as well as impaired mechanical properties.
Those problems are solved by the present invention, whose object is to provide polycarbonate resin compositions for optical uses with good mold release to facilitate production, good thermal stability, and very little discoloration during molding.